The Status of the Pierre Auger Observatory

Bruce DawsonUniversity of Adelaide, Australia

for the Pierre Auger Observatory Collaboration

Plan

• Description of the observatory• Physics aims• History and Schedule

• A Hybrid detector - why?

• Surface Detectors - Aperture and Resolution• Fluorescence Detectors• Hybrid Reconstruction - Aperture and Resolution

• First events and preliminary reconstruction

Data from Agasa: 100km² x 10 years

Physics issues with Auger:Physics issues with Auger:

• Where does the spectrum end ?Is there a GZK cutoff?Are the sources local (<150

Mly)?

• Primary nature (composition) ?Nuclei? Protons ?Gamma rays? Neutrinos?

Or...?

• What is the source of UHECR ?Bottom-Up or Top-Down

scenario ?

Northern hemisphereNorthern hemisphereMillard countyMillard county

Utah, USAUtah, USA

Southern hemisphere:

MalargüeProvincia dede

MendozaArgentina

Collaboration:Collaboration:>250 researchers from 30 institutions and 19 countries:Argentina, Armenia, Australia, Bolivia, Brazil, Chile, China, Czech Republic, France, Germany, Greece, Italy, Japan, Mexico, Poland, Russia, Slovenia, United Kingdom, United States of America, Vietnam

The Observatory

• Mendoza Province, Argentina

• 3000 km2, 875 g cm-2

• 1600 water Cherenkov detectors 1.5 km grid

• 4 fluorescence eyes -total of 30 telescopes each with 30o x 30o FOV

65 km

Pierre Auger - a major step

• Need high statisticslarge detection area : 2 x3000 km²

• Uniform sky coverage2 sites located in each hemisphere

Argentina and USA

• Hybrid detector : surface array (water Cerenkov tanks)

+ fluorescence detector Good energy and pointing resolution,

Improved sensitivity to composition

Energy cross calibration

History and Schedule

• August 1991 - concept born• October 1995 - base design complete• March 1999 - ground-breaking at southern site

History and Schedule

• January 2000 - beginning of construction• Feb 21, 2000 - deployment of first detector

• May 23, 2001 - observation of first fluorescence event• August 2, 2001 - first surface detector event observed

Schedule at Southern site

• 2000 and 2001 - “Engineering Array” 40 surface detectors and two fluorescence telescopes

• 2002-2004 - full production and deployment,and staged turnon of data-taking

Reason for winter slow-down

Engineering Array

Why a Hybrid Observatory?

• Hybrid resolution of arrival directions, energies and masses is superior to that achieved by the SD or a single FD eye independently

• Rich set of measurements on each hybrid EAS

• SD and FD measure cosmic ray parameters using different methods with different systematic errors– Cross-checks and control of systematics.

• while the FD only operates with a duty cycle of10%, the Hybrid observations will allow confident analysis of SD data taken without FD coverage.

e.g. Measurements of Energy

• SD alone: E from estimates of water Cherenkov density 1000m from the shower core– requires conversion factor from EAS simulations

• FD alone: E from estimates of energy deposition in the atmosphere (light dE/dX). – requires knowledge of atmospheric transmission.

• two methods can be compared with Hybrid – Checks simulations and measurement systematics

Surface Detectors

• for SD-only operation, typically will require 5 stations at the 4 vem trigger level (< 20 Hz per station)

• standard techniques for direction and core finding. Several LDFs under study, including a modified Haverah Park function.

• 10 m2, 1.2 m depth, 3 PMTs, 40 MHz FADC

• Integrated signal expressed in units of vertical equivalent muons (1 vem ~ 100 pe)

Three 8” PM Tubes

Plastic tank

White light diffusing liner

De-ionized water

Solar panel and electronic box Comm

antenna

GPSantenna

Battery box

Comms.Tower At Los Leonesfluorescencesite

Surface Detectors

• SD water Cherenkov detectors measure muon, electron and gamma components of EAS, the latter especially important at large core distances

1019eV proton

Surface Detector Resolution

• SD Angular resolution: E > 1019eV

(deg) Proton/Iron Photon

E>1019eV E>1020eV E>1019eV

20o 1.1o 0.6o 4.0o

40o 0.6o 0.5o 2.5o

60o 0.4o 0.3o 1.0o

80o 0.3o 0.2o 1.0o

space angle containing 68% of events

Surface Detector Resolution

• Energy determined from fitted density at 1000m, (1000). Conversion factor from simulations; averaged for p and Fe primaries. E > 1019 eV

rms E resolution ~12% (assuming p/Fe mixture)

Proton

Iron

photon

SD Aperture and Event Rate

• Zenith < 60o, based on AGASA spectrum (Takeda et al 1998)• (Zenith > 60o adds about 50% to event rate)

Eo (eV)Trig Aperture

km2srRate per year

> Eo

1018 0 0

3x1018 2200 15000

1019 7200 5150

2x1019 7350 1590

5x1019 7350 490

1020 7350 100

2x1020 7350 30

Auger Southern Site

• Hybrid reconstruction works when a shower is recorded by the surface array and at least one eye

• This multiple-eye design reduces our reliance on precise knowledge of atmospheric attenuation of light

• Mean impact parameter at 1019eV is 13km = Fluorescence site

The completed FD building will house 6 telescope/ camera arrays

Fluorescence Detector

Schmidt aperture stop

440 pixel camera 30ox30o

3.8m x 3.8m prototype mirrorand camera

Hybrid Reconstruction of Axis

• good determination of shower axis is vital for origin studies, but also vital as first step towards good energy and mass composition assignment

• use eye pixel timing and amplitude data together with timing information from the SD. – GPS clocks in SD tanks and at FDs.

• Hybrid methods using one eye give angular resolution comparable to “stereo” reconstruction

Hybrid Reconstruction (Cont.)

• eye determines plane containing EAS axis and eye – plane normal vector known to an

accuracy of ~ 0.2o

• to extract Rp andeye needs to measure angular velocity and its time derivative d/dt– but difficult to get d/dt, leads to

degeneracy in (Rp

• degeneracy broken with measurement of shower front arrival time at one or more points on the ground– eg at SD water tank positions

Hybrid Reconstruction (Cont.)

• Simulations at 1019eV• Reconstruct impact parameter Rp. Dramatic

improvement with Hybrid reconstruction

Single FD only

median Rp error = 350m

strong dependence on

angular “Track Length”

Hybrid

Simulated Hybrid Aperture

• Note the significant aperture at 1018eV, and the stereo aperture at the higher energies

• Trigger requirement: at least one eye triggering on a track length of at least 6 degrees; two surface detectors. < 60o

• Hybrid Aperture = Hybrid Trigger efficiency x 7375 km2sr

Hybrid TriggerEfficiency

“Stereo” Efficiency

Hybrid Reconstruction Quality

• 68% error bounds given• detector is optimized for 1019eV, but good Hybrid

reconstruction quality at lower energy

E(eV) dir (o)Core

(m)E/E (%) Xmax

g/cm2

1018 0.7 60 13 38

1019 0.5 50 7 25

1020 0.5 50 6 24

statisticalerrors only

zenithangles < 60O

Official ribbon cutting, Nov. 2000

Assembly Building

Open house for the public

Office Building Opening Nov 2001

“First Light” 23 May 2001

85 degree zenith angle event

Jan 6 2002

First 7-foldcoincidence

All tank signals sharp in time (asexpected)

“Gold”eventJan 172002

“Gold”eventJan 172002

Laser Shots

• Probing atmospheric transmission 300-400 nm• Calibration tool

YAG355nm6 microJ

Light scatteredtowards detector(Rayleigh, aerosol)

Laser Shots - calibration

• 355nm vertical laser 3km from detector

Black - real dataRed - simulation

Camera - Light Collection

Hybridevent.

SinceDec2001

Hybrideventrate ~ 1 pertwo hrs

Cerenkovcontaminated

Dec 12, 2001Hybrid trigger

43 fired pixelsin camera

Result of hybridgeometric reconstruction

zenith angle = 25.8 degcore distance =11300 m

collected charge(ADC units)vs time.Total time approx 20s

transformed toshower charged particle numbervs atmosphericdepth (g/cm2)

PRELIMINARY

Conclusion

• Engineering array is built and operating well.• second FD building being constructed now, first

site fully instrumented (6 telescopes) by Oct 2002.• next 100 SD installed starting Sep 2002• expect full observatory complete by last quarter

2004• but data will be pouring in well before from partially

completed system.

Neutrino detection

• Near horizontal air showers• Normal hadronic shower characteristics

– All EM component absorbed– Shower front very flat– Time spread in particle arrival times < 50ns

• Neutrino shower characteristics– Look like a normal shower, except horizontal– Large EM component– Curved shower front – Particle arrival time spread a few microseconds

Neutrino detectionCapelle,Cronin,Parente & Zas Astropart.Phys., 8 , 321 (1998)

Proton-blazar

Two cross sections

optimistic/conservative predictions

Yearly event rates, 3000km2 array

Neutrino detection - tau

• Standard acceleration produces very few tau neutrinos (nor do topological defects)

• But if transforms to with full mixing, then at Earth, e :: goes from 1:2:0 to 1:1:1

• a particle can escape from deep in rock and decay in air, producing a normal-looking hadronic shower. Expect upward showers from within 5 degrees of horizontal.

• Find 90% of signal comes from “upward” events, and 10% from “downward” from mountains around array

Bertou, Billoir,Deligny,Lachaud,Letessier-Selvon, astro-ph/0104452